When high-hardness materials to be rolled, such as stainless steel, are cold rolled, small diameter work rolls are adopted in a rolling mill. There is a Sendzimir mill as a representative of such rolling mills.
FIG. 1 is a block diagram showing a general Sendzimir mill with 20 rolls. The Sendzimir mill shown in FIG. 1 has a roll arrangement made up of work rolls 2 and 3 in a top and bottom pair, first intermediate rolls 4 to 7 in quantities of two each on top and bottom, second intermediate rolls 8 to 13 in quantities of three each on top and bottom, and backing bearings 14 to 21 in quantities of four each on top and bottom.
Each of the backing bearings 14 to 21 is provided with an eccentricity mechanism, and the position of each of the rolls 2 to 13 is determined by the setting of each eccentric angle of the backing bearings 14 to 21. Each eccentric angle of the backing bearings 14 to 21 is adjusted by a plurality of screw down devices arranged above and below. Concretely, the screw down devices are composed of a top screw down device 22, a bottom screw down device 23, top side screw down devices 24 and 25, and bottom side screw down devices 26 and 27.
On a Sendzimir mill having the above-described arrangement, before the start of rolling, the setting of each of the screw down devices 22 to 27 has hitherto been carried out in the method described below.
That is, each eccentric angle of the backing bearings 18 to 21 is determined so that the bottom work roll 3 maintains pass line, and set by the bottom screw down device 23 and the bottom side screw down devices 26 and 27.
On the other hand, the top screw down device 22 is used to obtain desired thickness. That is, the eccentric angle of the backing bearings 15 and 16 is adjusted by the top screw down device 22 by constant load control so that the rolling load (or pressure) obtains a preset value. Incidentally, after the start of rolling, the eccentric angle of the backing bearings 15 and 16 is appropriately adjusted by gauge control which involves adjusting the gap between the work rolls on the basis of measured thickness values measured by thickness meters.
That is, the top screw down device 22 is not operated on the basis of the preset value of the eccentric angle of the backing bearings 15 and 16, which is not calculated actually. Therefore, it is impossible to know the eccentric angle of the backing bearings 15 and 16 before a screw-down is performed actually. Incidentally, the eccentric angle of the backing bearings 15 and 16 varies also depending on the setting of the eccentric angle of the backing bearings 14 and 17 which is adjusted by the top side screw down devices 24 and 25.
And in a conventional method, the same value was used as the preset values of the four side screw down devices 24 to 27 in consideration of symmetricity. For this reason, the eccentric angle of the backing bearings 14 and 17 was set at the same value as the eccentric angle of the backing bearings 18 and 21 adjusted by the bottom side screw down devices 26 and 27. Due to such circumstances operation has sometimes been carried out with the eccentric angle of the backing bearings 15 and 16 undesirable setting.
Also, as a conventional art, there has been proposed a roll position setting method which involves setting the position of each roll of a Sendzimir mill also in consideration of the eccentric angle of backing bearings by a top screw down device (refer to Patent Document 1, for example).
Concretely, in the roll position setting method described in Patent Document 1, first, the eccentric angle by the top screw down device is determined so that the relation between the cylinder position of the top screw down device and the work roll position be linear. Next, the eccentric angle by the top and bottom side screw down devices are determined to satisfy roll gap, which is given by another calculation, based on the geometric relation of the top side roll set. Lastly, the eccentric angle by the bottom screw down device is determined from a simplified expression on the basis of that by these side screw down devices. And the above-described calculations are repeated until a solution which meets these conditions is obtained.    Patent Document 1: Japanese Patent Laid-Open No. 10-263638